One known fuel injector, described in German Application No. DE 10 2004 002 134, has a hydraulic coupling mounted between a valve needle and a piezoelectric actuator, which has a housing pot having a pot bottom and a lateral pot surface, and a piston that is axially displaceable in the housing pot. Between the piston and the pot bottom there is a coupler gap filled with fluid. On the outer side of the pot bottom, facing away from the piston, there is a first diaphragm made of steel, which, together with the pot bottom, encompasses a fluid-filled compensation space. In this context, the first diaphragm covers the pot bottom and is fastened at its edges to the pot bottom by welding. The compensation space is flow-connected to the coupling gap via a throttle element situated in the pot bottom. A second diaphragm made of steel covers an annular gap present between the lateral pot surface and the piston, at the end face of the housing pot facing away from the pot bottom. The annular diaphragm is fastened with its outer diaphragm edge to the lateral pot surface and with its inner diaphragm edge to the piston, by welding. To generate an overpressure in the compensation space, there is a helical compression spring which is supported in the valve housing, having axially directed spring force onto the first diaphragm, a pressure distribution disk being inserted between helical compression spring and the first diaphragm, which lies against the central region of the first diaphragm using a centrical elevation.